The problems suffered by libraries and archives holding ancient documents are mainly centred on their conservation and preservation, in order to achieve their durability over time; these conditions are not satisfied in almost any library or archives, so that more expedite actions are required aimed at a suitable restoration.
As most restoration methods are manual, they are slow and expensive. The cost of C=restoring damaged books and documents can be prohibitive, except for incunabular manuscripts or rare volumes which are priceless for documentary, aesthetic or historical reasons.
One of the most pressing problems in conservation of paper in books and other cellulosic materials (fabrics, documents, newsprint, etc.) is the acidity of the paper, which is a result of the nature of paper obtained from cellulosic fibres obtained from wood with additives such as alum or resin, and the action of external agents such as heat, acidic pollutants, ozone, high humidity and temperatures. Acidity is one of the culprits of paper destruction. Thus, as of a decade ago, research has been conducted in developing mass deacidification methods to save large document records which are endangered by the acidic paper problem suffered mainly by late 18th Century, 19th and 20th Century paper.
Mass deacidification methods previously tested coincide in their objective of reducing costs with results which are different from those obtained by manual restoration. An hourly wage for a restorer's work in Spain is between 1,800 and 2,000 Pta. in official restoration centres, while a 500 page book requires approximately 70 hours, plus another 15 for sewing and binding. Therefore, a restorer-binder working 1,750 hours a year using odd moments to bind can restore about 20 books a year (between 175,000 and 158,000 Pta./book). These figures make a global restoration policy unviable.
Certain mass deacidification methods have been developed, but it can be said that none of the techniques offered fully satisfies the recommended quality criteria, such as preselection of the material to be restored, predrying, duration of the treatment, effect on ink, colours, covers, neutralisation of the paper acidity, final pH, alkali reserve, health risks to operators and readers, environmental impact, cost of the equipment and cost of treatment.
The present state of the art is described among other documents in Patent application PCT WO 90/03466, by the Lithium Corporation of America, which describes a mass treatment method for cellulosic matter which comprises deacidification of the paper, consisting of placing the paper in contact with solutions in hydrocarbons or halochlorocarbons of certain magnesium methoxy- and butoxy-polyethyleneglycols treated with carbon dioxide to provide low viscosity solutions which are more stable with humidity.
In an article by Dr. Robert S. Wedinger in Restaurator, Vol. 12, pp 1–17 (1991), a mass deacidification technique is described which consists of developing a number of compounds for simultaneous deacidification and strengthening of paper. The specific compound employed is carbonated magnesium butoxytriglycolate (MG-3) which neutralises the acidic components of paper. This process was discontinued in 1997 among other reasons due to the slow diffusion of the reagent and interactions between glycols and cellulose (R. Areal, J. M. Gibert and J. M. Dagá, The Effect of Aqueous Solutions of Alkoxypolyethylene glycols on the Mechanical Properties of Paper; communication in the Interim Meeting of the ICOM-CC Working Groups 20–22 April 1998. Graphic Documents. Stugard. Ludwisgsburg, Germany; and R. Areal, J. M. Gibert and J. M. Dagá, The Effect of Aqueous Solutions of Alkoxypolyethylene glycols on the Mechani-cal Properties of Paper, in the journal Restaurator, 19, 187–211, (1998). These reagents are not related to the invention described hereunder. They have been tested in the inventor's laboratories and an increase in cellulose volume has been shown to take place due to elimination of hydrogen bridges in the cellulosic material, and swelling of the pages, with an increased page thickness when measured with a micrometer. Tensile strength is also reduced with the accelerated aging of the paper, so that the results obtained from using these reagents are not too reliable.
In an article by Peter Schwerdt, in Sauvegarde et Conservation, Actes des Journées Internationales d'Études de l'ARSAC, Paris 30 Sep.–4 Oct. 1991, pp 213–216, a mass deacidification system is described for the Deutsche Bibliothek of Leipzig, comprising the following treatment stages for acid books and papers: predrying, deacidification, drying.
Patent application PCT WO 91/04800 (FMC Corporation) and U.S. Pat. No. 5,282,320 (Wedinggwe et al.) describe a machine with a size implying that it cannot be moved, as a book factory, lacking means for efficient dosing and double treatment autoclaves.
U.S. Pat. No. 5,120,500 (Batelle Institute) describes a process for non-polluting deacidification of books and other paper and printed matter of a size similar to that of the FMC design, so that it is a restoration installation comprising a predrying process for these products using high frequency radiation in a vacuum, treatment with solutions for deacidification and later elimination of solvents by vacuum drying with high frequency radiation again. This last type of predrying and final drying have been replaced by conventional means employing heat and vacuum due to the alterations of book pages caused by microwaves, as a result of the mobility of metal particles attached to the surface of the pages. It employs hexamethyl-disiloxane as a solvent and an adduct formed by magnesium ethoxide and titanium ethoxide as deacidifying agents. Predrying time is not indicated. The system is not globally related to our invention.
Patent GB 1,582,265 (Batelle Ingenieurtechnik) describes a process in which aged, damaged and fragile paper is treated with a solution containing isocyanate or isocyanate vapour, preferably using isocyanate with two or more isocyanate groups. This system is not related to out invention.
A publication by James Stroud, The Paper Conservator, Vol 18, 57–70, (1994), describes a deacidification process using diethylzinc (DEZ) which requires a 5-stage treatment: dehydration, impregnation, stabilisation, rehydration and post-treatment at 1 atm. The first two stages take place in a vacuum chamber; the rest of the process takes place at atmospheric pressure, and the entire process may last up to 5 days. Currently, the DEZ project is not in service and although work is being carried out to solve its inconvenients, persons in charge of the project do not expect it to be operational until the year 2003.
In the book “BOOK PRESERVATION TECHNOLOGIES”, U.S. Congress, Office of Technology Assessment. Washington, D.C.; U.S. Government Printing Office, May 1988 are described several different problems and solutions related to this topic.
A further process with a certain reliability is Bookkeeper from Preservation Technologies, Inc., which uses magnesium oxide with particle size between 0.2 and 0.9 microns and a surfactant acting as a dispersant of the magnesium oxide in the solvent, with perfluoroheptane as solvent. The process consists of a pre-treatment, impregnation and posttreatment. This last procedure is without a doubt one of the most promising ones currently due to the successive evaluations and revisions made on it; the experience of its researchers show that this process, as it employs a microdispersion of magnesium oxide whose a transverse penetration in the paper depends of the number of loops of the magnesium oxide, in glossy paper the oxide particles remain on the surface and have little penetration into the paper, as indicated in the examples of an application of the method disclosed by the inventors in patent application PCT WO 00/08250. Preparation of the magnesium oxide and its application are described in U.S. Pat. No. 4,522,843.
The pioneering process is the Canadian Wei T'o, which gives good pH results but not so good results for homogeneity of the alkaline reserve, which due to the low solubility of the reagents in methanol produce side effects on inks; the alkaline reserve which remains in the paper after the process is relatively low, so that after a generally short time it is again necessary to deacidify.
The Sablé process is a variation of the Wei T'o method; its disadvantages is that printed ink will run and white dust is deposited on the bindings. The total alkaline reserve and its distribution is unsatisfactory.
Among the antecedents in the state of the art is also Spanish Patent No. ES 2,125,792, in the name of the applicant, which relates to a device and method for mass deacidification disinfestation and disinfection of documents and books, employing a solution of a reagent and a suitable solvent HFC R134a; reagents are methoxy and butoxy polyethyleneglycolate magnesium carbonates, which reagents are very similar to those used by the Lithium Corporation of America, but as they were shown to give unsatisfactory results they were discarded after their application in the patented device and replaced by other products. Spanish patent application P9700964 in name of the applicant is a modification of Spanish Patent No. ES 2,125,792.
The above method presents difficulties in the impregnation stage due to an impregnation time of 3 hours, but as the solvent distillation stage takes place in the same autoclave, during said distillation a time increase takes place on the order of 4 to 6 hours depending on the amount of solvent; this defect may not be corrected in this method.